Dual fuel nozzles employed in the combustion section of a gas turbine are well known in the art. Dual fuel nozzles are employed to atomize a liquid fuel to enable a gas turbine to operate more effectively and improve the start-up reliability of the combustion turbine. The atomization of a liquid fuel consists of breaking down the liquid fuel into fine particles to form a spray that can be combusted after the mixture is ejected out through the nozzle.
In a dual fuel nozzle, high-temperature atomizing air is used in conjunction with the flow of a liquid fuel to start up the combustor. The liquid fuel is ejected through a nozzle as an atomizing air flow is directed at, and strikes, the liquid fuel at a relatively high-temperature and high-pressure. When the atomizing air impacts the liquid fuel, the liquid fuel is broken down into relatively smaller particles to form a combustible spray which is easily combusted in the combustor section of the gas turbine.
A conventional dual fuel nozzle assembly 20 coupled to a gas turbine 22 is shown in FIG. 1. The conventional dual fuel nozzle assembly generally comprises a main nozzle body 24, spacer collar 26, and unitary atomizing air and liquid fuel member 28. The main nozzle body 24 and unitary atomizing air and liquid fuel delivery member 28 are coupled together with the spacer collar 26 therebetween.
The main nozzle body portion 24 comprises a flange portion 30 and a gas supply portion 32. The flange portion 30 is adapted to be mounted to the gas turbine 22. The main nozzle body portion 24 defines a centrally disposed bore 34 that extends from the flange portion 30 and through the gas supply portion 32 for receiving the unitary atomizing air and liquid fuel member 28.
Referring to FIG. 2, the prior art unitary atomizing air and liquid fuel member 28 is shown in more detail. The unitary atomizing air and liquid fuel member 28 has a inlet end 36 and discharge end 38. The unitary atomizing air and liquid fuel delivery member 28 comprises a nozzle flange portion 40, outer wall 42, inner wall 44, liquid fuel pipe 46, nozzle tip 48, lap joint 50, and swirl cap 52. The nozzle flange portion 40 further defines an atomizing air supply channel 54.
The unitary atomizing air and liquid fuel member outer wall 42 is concentrically disposed about the inner wall 44. The outer wall 42 is spaced apart from the inner wall 44, thereby, defining an atomizing air flow passage 56 which is in fluid communication with the atomizing air supply passage 54. A conical end portion 60 of the outer wall 42 proximate to the discharge end 38 is adapted to securely receive the swirl cap 52.
The inner wall 44 defines a bore 62 for receiving the liquid fuel pipe 46. A portion of the inner wall 44 proximate to the discharge end 38 is adapted to securely receive the nozzle tip 48. The nozzle tip 48 is seated adjacent to the swirl cap 52, with the lap joint 50 therebetween.
When a turbine starts-up on a relatively heavy fuel, combustion air having a temperature of approximately 100.degree. F. surrounds the outer wall 42 of the unitary atomizing air and liquid fuel delivery member 28. The inner wall 44 of the air and fuel delivery member 28 is subjected to a flow of liquid fuel having a temperature of about 200.degree. F. The differences between these temperatures may cause the nozzle tip 48 to expand axially into the lap joint 50 and swirl cap 52, and over the axial extent of the tube, results in the loss of the lap joint 50 and damage to the swirl cap 52.
It would therefore, be desirable to provide a nozzle assembly that provides improved integrity.
Because unitary atomizing air and liquid fuel supply member 28 employed in dual fuel nozzle assemblies 20 cannot be disassembled, neither the nozzle tip 48 nor swirl cap 52 can be replaced or repaired when necessary. It would, therefore, be desirable to provide a dual fuel nozzle that can be repaired.
Another problem that may arise during the operation of a dual fuel nozzle 20 is that the nozzle tip 48 may become clogged when a residuum of liquid fuel remains in the nozzle tip or liquid fuel passage 58 and is subjected to long periods of heat soaking. As the residuum is exposed to heat over a certain period of time, the residuum forms deposits of gums, carbon, and varnish. These deposits end up clogging the orifices in the nozzle tip 48, thereby, constricting the fluid flow through the nozzle tip 48. Once the fluid flow is constricted, however, the nozzle tip 48 cannot be replaced or repaired because the unitary atomizing air and liquid fuel delivery member 28 cannot be disassembled to gain access to the constricted area.
It would, therefore, be desirable to provide a dual fuel nozzle that is relatively easy to maintain.